I would either look locally or build one yourself if you feel up to it. Also, I would try to get the best parts you can now rather than an average piece so it's better equipped to handle new games for a longer time.
It's a good idea to build your own computer because you know exactly what parts are in the computer and how you configured it. I also agree that it's a good idea to future proof your PC so you won't have to update the components every so often. I built a budget $600-$700 PC back in 2012 and it runs Trainz 2010 with decent fps.